Topic: Carb experts chime in

[CBXJOHN]

Two bikes, similar problem. I purchased a '75 750K a few months ago, just got it on the road. It had rebuilt carbs and was road ready according to the owner. At the same time, I was prepping a '76 Cb 550 for a customer. This bike had not been used in 20 years, gummed carbs, gooey brakes, I'm sure you know the drill. I rebuilt the carbs, I installed kits with new needles, mains, slow jet, flort needles, gaskets etc. I set the floats with precision (I'm a toolmaker) and of course, set the main needles/clips to the correct slots according to the book. My intake boots are good, and the air filter boots new (Thanks Paul Gabor).

Overall, the bike runs well, but it seems flat on the low end off idle. Ironically, my CB 750 feels the same. I live in an area that is roughly 2500' above sea level, would that be enough to effect my needle settings? Should I lean it by lowering my needles one step? Also, would adjusting the air screws help, or are they just for idle tuning. Thanks ahead for  the advice.

Both bikes ran better in certain areas , typically as I descended into the valley throttle response was better. I have other carbureted bikes, '81 CBX, '89 NT 650, '86 XL 600R, they run great. Any help advice/would be appreciated.

John

[MRieck]

 What "carb kits" did you install?

[CBXJOHN]

This is the EXACT kit I used:

http://carbkitscapital.com/carb_kit_list_model.php?make=Honda&model=CB550

Oh yes, their kits are made by KEYSTER.

Usually, I re-use the original pieces, I figured I could save some time by ordering kits, because cleaning slow jets, diffusers, and float inlets is laborious work and they need to be PERFECT to work properly.

John

[flybox1]

Many have had issues with Keyster kits.  needles are of a different taper than OEM causing fuel atomization issues.
if you still have them, put your originals back in.   
after that, adjusting the AF screws WILL help lean your idle mixture, just be sure that the idle circuit was cleaned properly (by you) and as a second step, drop you needle clip setting to adjust for your altitude.

[ekpent]

Some of those carb rebuild kits are total JUNK.Removed some "new" #40 slow jets from a new arrival that were HUGE compared to the stock Kehins.Save your money and re-use the good old stock stuff. Maybe Mike knows a source for the good stuff?

[CBXJOHN]

Well,
   I'm stuck with the stuff, the old parts were tossed in the bench cleanup. Thanks for the advice. I did turn my airscrews another 1/4 turn in, thus richening the mixture off idle. That makes it a total of 3/4 turn out. The original setting I used from the manual on the website here was 1 3/8 turns out, I had re-set them to 1 turn yesterday, now 3/4 this AM. The throttle responds much better than before, I will try it on the road later.

 When I did install the parts, I miked the main needles, size wise, the replacements were pretty close. I can accelerate up to redline no problem, my problem seems off idle. it may just be the airscrews, I hope so, I don't want to pull the carbs again, I'm getting killed $$$ wise on this job.

John